I know there's a whole post already about this but it's about to go nuclear before long. I just wanted to post a list of where it is illegal to leave your child in the car alone, as a reference. It was brought up in the Piggyback post.
Washington -illegal to leave children under 16 years old unattended in a car that is running, in a public place
California - illegal for caregiver to leave a child ages 6 years or younger alone in a vehicle without supervision of person over age of 12 when engine is running or keys are in ignition or there are risky conditions present
Florida - illegal to leave child younger than 6 in car with motor running at all; or for more than 15 minutes when car is not running
Illinois - illegal to leave child in car unattended for more than 10 minutes
Maryland - illegal to leave child under the age of 8 in car unattended if car is out of sight of the responsible adult
Michigan - illegal to leave child under the age of 6 for period of time that results in "unreasonable risk of harm or injury to the child."
Nevada - illegal to leave child of 7 years or younger unattended by someone over age of 12 if the motor is running or the situation is risky/dangerous.
Oklahoma - illegal to leave child 6 years or younger "unattended" - with unattended defined as "beyond a person's direct ability to care for or come to the aid of the unaccompanied person" if conditions (e.g. extreme weather, inadequate ventilation) pose a risk to the safety of the child.
Connecticut - illegal to leave child under age of 12 in a place for a "period of time that presents a substantial risk to the child's health or safety ...."
Hawaii - illegal to leave child under the age of 9 car alone for more than five minutes.
Louisiana - illegal to leave child under age of 6 when car operator is more than 10 feet away from vehicle.
Pennsylvania - illegal to leave child under 6 years alone in car when vehicle is "out of the person's sight" and under dangerous circumstances - if they are on public roads and traffic ways, including parking lots.
Tennessee - illegal to leave a child under age of 10 alone in car
Texas - illegal to leave child under the age of 7 alone in car for more than five minutes